Dual power supply 3V,5V,6V,9V,12,15V with LM317,LM337

Here is the variable dual lab power supply circuit.You can select voltage levels are 3V,5V,6V,9V,12,15V at 1A
and -3V,-5V,-6V,-9V,-12V,-15V at 1A, use IC LM317 (for positive volt) and LM337 (for negative volt), Controls Voltage Output by S2 For +Vout and S3 for -Vout.
The transformer is 2A size. And the both IC holds heat sink.
Read detail more in circuit.

Our friends is looking for a dual power supply positive, negative and ground for a experiments various circuits.
In some times we need to have experiments about a OP-amp IC – LM741. Which must to use level voltage power supply of +9 volts and -9 volts, or when we a preamplifiers circuit or tone control circuits but they uses supply voltage of +15 volts and -15 volts
We think this circuit will respond your needs certainly because….
- Can provide the positive, negative voltage at size 3, 5, 6, 9, 12 and 15 volts respectively and the current output under 1.5 amps.
- Easy to use with rotating selector switch to selects level voltage as you want, Do not have a voltsmeter measure the output voltage.
It is circuits simple and cheap to make because the IC that have been popular are LM317 and LM337.

How it works
As show figure below , there are the didoe 1N4001 – D3 and D4 acting full-wave rectifier side the positive voltage. Then so filter waveform to smooth with a capacitor C1(2,200uF) , Then entered to input of IC1(LM317T) that is a positive regulated IC, it can adjust voltage to changing of 1.2-37 volts and provide the maximum output current of 1.5 amps

-The output voltage can change as value of resistor R2 and changes resistanes of R3 to R8, by selector switch S2 to choose the resistance as you want , to we have a voltage level from 3, 5, 6, 9, 12 and 15 volts.
-The capacitor C7(22uF) is determined an impedance and reduce a transient on output of IC1-LM317T
-The capacitor C3(0.1uF) is used when we install the IC1 far from C1 too much.
-The capacitor C5(22uF) act reduce the ripple signal before it is amplified when the high output voltage up.
-For the capacitor C9 that act reduce the ripple that appear on the output.
-Both diode(1N4001) D5 and D7 for protects the IC1 from discharging of C7 and C5 when the input is shorted circuit.
-The negative section like the positive as above . The diode D1 and D2 are rectifier diode in full wave negative model, by has IC2-LM337T is the negative DC regulated IC. For all resistors and capacitors that also act as same as the positive as described above

Sir,Im John from the Philippines, my question is? If I only need the positive side IC1-LM317T, what arrangement or adjustment of diagram will be made for us to assure that it will work as well, can we erase or not include the lower part of the diagram?